Simple implementation in C using stack in O(n) time. Do ask for any clarifications.

#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>

int main() {

char string[101];
scanf("%s",string);
//printf("%s",string);
char *stack=(char *)malloc(sizeof(char)*strlen(string));

int top=-1;

for(int i=0;i<strlen(string);i++){

    if(i==0)
        stack[++top]=string[i];
    else
        {
        if(stack[top]==string[i])
            top--;
        else
            stack[++top]=string[i];


    }



}
if(top==-1)
    printf("Empty String");
else
    {
    for(int i=0;i<=top;i++)
        printf("%c",stack[i]);
}



return 0;
}